Tech giant Google recently announced it would purchase renewable wind energy to help power one of its data centres in Mayes County, Oklahoma. The agreement marks the latest milestone in Google's mission to maintain a zero carbon footprint, a goal it says it reached in 2007.

To hit this mark each year, besides using clean energy where possible, the company supports projects that produce carbon offsets and works to improve the energy efficiency of its worldwide mega data centres, which handle 3bn search queries daily, support 425m Gmail users and account for about 85% of Google's total carbon footprint.

A focus on efficiency has been part of Google's approach from the beginning, says Joe Kava, the company's senior director of data centre operations, during a recent interview on the Google campus in Mountain View, California.

Founders Larry Page and Sergey Brin understood early on that building a computer network to organise the world's information would consume a vast amount of energy, especially if they used off-the-shelf computer servers available at the time. Kava says commercial servers of the day were not designed for the work Google needed to do, nor optimised for energy efficiency.

As a consequence, "money you are spending in overhead and wasted energy is just thrown away; it's not doing us any good and it's not doing the planet any good," says Kava.

Instead, Google designed their own computer servers and the large warehouse-like spaces to hold all them. Today, Google shares these technical details selectively. Still, its decision-making process , as described by Kava, provides some useful insights for any business looking to reduce waste and trim carbon impacts.

Challenge conventional wisdom

Current estimates suggest that the world's data centres are consuming about 2% of the electricity generated each year. But at many data centres, up to half of this energy is being used to cool the servers or on other overheads rather than actually processing data.

When Google began designing their own centres, they discovered that much of this cooling was unnecessary. "Lots of specifications for data centres go back to mainframe days when computers were still using punch cards," says Kava, "so most companies over cool their centres."

Google has a simple test to make sure the data server rooms don't get too cold and waste energy unnecessarily. Employees who maintain the systems wear shorts, rather than long trousers, at work. If the data centre becomes uncomfortably cool for shorts-wearing workers, the temperature is too low.

By rethinking many long-accepted practices, like cooling requirements, Google says its data centres are able to use 50% less power than the industry average.

Rely on natural systems whenever possible

Another technique for saving energy is to locate the data centres near natural sources of cool air or water whenever possible, says Kava. For example, the company completed installation of a data centre in Finland last year by refitting an old paper mill. The building's air-cooling systems will rely completely on cold, and free, seawater from the nearby Bay of Finland.

Co-operate with local communities

In Douglas County, Georgia, Google built its own water treatment plant that allows them to recycle wastewater obtained from the county for cooling its facility rather than taking valuable drinking water from the community. In a second phase of the process, Google cleans the water again before returning it to the nearby Chattahoochee River.

"The payback for this system is longer than we normally see," says Kava, "but management decided it was the right thing to do for the environment and the community."

Share what you know

Google has long considered its unique data centre designs as a key competitive advantage. For much of the last decade, the company was notoriously tight lipped about these advances, disappointing some in the industry who believe best practices should be shared when it comes to environmental issues.

Starting in 2008, Google began to publicise the energy efficiency numbers for its data centres, which it felt were industry leading at the time, using the standard industry metric of Power Usage Effectiveness (or PUE). Along with these numbers, the company shared some of the details about the designs that allowed them to achieve these levels.

The sharing continued in 2009 and 2011, when Google hosted data centre efficiency summits bringing together others in the industry. Google has since created a best practice website, which is aimed primarily at smaller companies who don't have the resources to build their own data centres from the ground up and are likely using commercial off-the-shelf equipment.

"A lot of these smaller data centres may be in a room in an office building where they feel like they are constrained from making modifications," says Kava. But there are a lot of simple things that these companies can do with quick paybacks that will improve efficiency, he adds.

Most recently, Google took another step forward on its transparency journey, launching a new website that gives a first-time, behind-the-curtain look at its data centre operations.